In recent years, various kinds of electric equipment are controlled by an inverter circuit in view of environment protection, to save energy and achieve high efficiency. In particular, an automobile industry is introducing to market a hybrid electric vehicle (hereinafter, referred to as “HEV”) which is driven by an electric motor and an engine; thus, technique which is benign to earth environment and realizing energy saving and high efficiency is actively developed.
A working voltage of an electric motor for such an HEV is high, e.g., several hundreds volts. Due to the high voltage, a metallized film capacitor having electric properties, such as a high withstanding voltage and a low loss, is getting an attention as a capacitor to be used for the electric motor. A maintenance-free product is a recent demand in the market, hence allowing the metallized film capacitor having an extremely long life to be remarkably used.
In general, such metallized film capacitors are mainly classified into a structure in which a metal foil is used as its electrode and another structure in which a vapor-deposition electrode formed on a dielectric film is used as its electrode. In the case of the metallized film capacitor using a metal vapor-deposition electrode that is an electrode made of vapor-deposited metal, the volume occupied by the electrode can be reduced more than an electrode made of a metal foil so that a light-weight device having a small size can be achieved. In such a metal vapor-deposition electrode, in the event of occurrence of short-circuit at a defective insulation portion, a portion on the periphery of the defective portion is evaporated and scattered by energy of the short-circuit to have an insulating property. Thus, the metal vapor-deposition electrode has a self-recovering function for recovering the functions as a capacitor. Since the self-recovering function provides high reliability against insulation breakdown, the metal vapor-deposition electrode has been widely used.
FIG. 12 is a cross-sectional view of conventional metallized film capacitor 501 described in Patent Literature 1. FIG. 13 is a plan view of metallized films 502 and 503 used in metallized film capacitor 501.
Metallized film 502 includes dielectric film 33A made of, e.g., a polypropylene film and metal vapor-deposition electrode 31A provided on a surface of dielectric film 33A. Metal vapor-deposition electrode 31A is formed on one surface of dielectric film 33A by vapor-depositing aluminum except for insulating margin 34A on one end of dielectric film 33A. Metallized film 503 includes dielectric film 33B made of, e.g., a polypropylene film and metal vapor-deposition electrode 31B formed on one surface of dielectric film 33B. Metal vapor-deposition electrode 31B is formed on one surface of dielectric film 33B by vapor-depositing aluminum thereon except for insulating margin 34B on one end of dielectric film 33B. Metallized films 502 and 503 are stacked and rolled. Sprayed-metal electrodes 36A and 36B are formed on both end surfaces of rolled metallized films 502 and 503. Metal vapor-deposition electrodes 31A and 31B are connected to sprayed-metal electrodes 36A and 36B and drawn out, respectively.
Portions of metal vapor-deposition electrodes 31A and 31B facing across dielectric film 33A constitute an effective electrode portion forming a capacitance. The effective electrode portion has width W in a direction in which sprayed-metal electrodes 36A and 36B are arranged. Metal vapor-deposition electrode 31A is divided by slits 35A into plural divided electrode portions 32A within on the side from the center of width W of the effective electrode portion toward insulating margin 34B. Metal vapor-deposition electrode 31B is divided by slits 35B into plural divided electrode portions 32B on the side from the center of width W of the effective electrode portion toward insulating margin 34A. Slits 35A and 35B are formed by oil transferred onto dielectric films 33A and 33B. Metal deposition electrodes are not formed at slits 35A and 35B on dielectric films 33A and 33B.
Metal vapor-deposition electrode 31A is located on a side closer to sprayed-metal electrode 36A opposite to insulating margin 34A from the center of width W of the effective electrode portion, and is formed on the entire portion on one surface of dielectric film 33A. Metal vapor-deposition electrode 31B is located on a side closer to sprayed-metal electrode 36B opposite to insulating margin 34B from the center of width W of the effective electrode portion, and is formed on the entire portion on one surface of dielectric film 33B. Plural divided electrode portions 32A are connected to metal vapor-deposition electrode 31A with plural fuses 37A in parallel with one another, respectively. Plural divided electrode portions 32B are connected to metal vapor-deposition electrode 31B with plural fuses 37B in parallel with one another, respectively.
Metallized films 502 and 503 are stacked on each other and rolled by plural turns. Melting zinc is sprayed on both end surfaces of rolled metallized films 502 and 503 to form sprayed-metal electrodes 36A and 36B, thus providing metallized film capacitor 501.
Metallized film capacitor 501 has a self-protective function so that little amount of heat generation is caused by fuses 37A and 37B. A current flowing into portions of metal vapor-deposition electrodes 31A and 31B as being closer to sprayed-metal electrodes 36A and 36B, and the current is smaller as being farther from sprayed-metal electrodes 36A and 36B. Metal vapor-deposition electrodes 31A and 31B that are closer to sprayed-metal electrodes 36A and 36B than divided electrode portions 32A and 32B are have larger areas. Therefore, metal vapor-deposition electrodes 31A and 31B have smaller resistance so that large heat is not generated even when a large current flows. A smaller current flows into divided electrode portions 32A and 32B that are farther from sprayed-metal electrodes 36A and 36B than metal vapor-deposition electrodes 31A and 31B are. Therefore, currents flowing through fuses 37A and 37B are smaller so that heat generated by fuses 37A and 37B can be reduced to consequently suppress a temperature rise.
In the case that metallized film capacitor 501 is used in an HEV, there are strong demands for, e.g., a high voltage resistance to applied voltage, a large electric current application, and a large capacitance. Therefore, plural metallized film capacitors 501 are connected in parallel with one another with bus bars. A case mold type capacitor including plural metallized film capacitors 501 accommodated in a case and a molding resin filling the case has been developed and put into practical use.
FIG. 14A is a cross-sectional plan view of conventional case mold type capacitor 504 described in Patent Literature 2. FIG. 14B is a cross-sectional view of case mold type capacitor 504 on line 14B-14B shown in FIG. 14A. Case mold type capacitor 504 includes case 41 made of a resin and plural capacitor elements 42 accommodated in case 41. Each capacitor element 42 is, for example, metallized film capacitor 501 shown in FIGS. 12 and 13. Connecting members 43A and 43B are unitarily coupled to each other. Connecting member 43A is accommodated in case 41 while connecting member 43B is externally drawn from case 41. Molding resin 44 filling case 41 fixedly secures capacitor elements 42, and is made of an insulating resin, such as an epoxy resin. Case mold type capacitor 504 further includes electrode unit 45 and mounting leg 46 for use in externally attaching case mold type capacitor 504. Molding resin 44 is injected into case 41 from injecting surface 47.
Connecting member 43A is connected to electrode unit 45 of each capacitor element 42. By coupling connecting member 43B that is unitarily coupled to connecting member 43A to an external apparatus, electrode unit 45 is electrically connected to the external apparatus. Case 41 accommodating the entire capacitor elements 42 and connecting member 43A therein is filled with molding resin 44 so that the entire capacitor elements 42 and connecting member 43A are secured. Injecting surface 47 is an opening surface of case 41 before the filling of molding resin 44. By injecting molding resin 44 from the opening surface, injecting surface 47 is formed. Connecting member 43B is externally drawn out from injecting surface 47, and directed outside of case 41.
Conventional case mold type capacitor 504 suppresses inductance without increasing the entire height.
In the case that case mold type capacitor 504 is used for a hybrid automobile, in particular, a high moisture resistant performance is required in addition to small-size and light weight as well as low costs. Upon application under the high-temperature and high-humidity environment, a leak current in metallized film capacitor 501 serving as capacitor element 42 becomes greater, and the capacitor performances tend to be subsequently lowered. Therefore, countermeasures, such as an increase of the amount of molding resin 44 of case mold type capacitor 504, are required, with the result preventing a small-size and a light weight as well as low costs.